(1) Field of the Invention
The present invention relates to a device element for effecting phase control and in particular to a photocoupler capable of performing phase control with a single device element.
(2) Description of the Prior Art
First of all, a configurational example of a phase controlling circuit using a conventional photocoupler will be described with reference to drawings.
1) FIG. 1 shows a phase controlling circuit which is composed of an a.c. power supply 51, a load 52 and a bidirectional tri-terminal switch 53, all connected in series and the bidirectional tri-terminal switch 53 is varied in its turn-on timing to thereby perform phase control. This bidirectional tri-terminal switch 53 is supplied with an output from a photocoupler 54 as a trigger signal. The photocoupler 54 outputs the trigger signal when a pulse is launched by a zero-volt detecting circuit 55, a controlling circuit 56 and a delay trigger circuit 57. This pulse signal is outputted from the delay trigger circuit 57, at a time delayed with a delay instructed by the controlling circuit 56 from a referenced zero-volt timing detected by the zero-volt detecting circuit 55. In other words, the turn-on timing of the bidirectional tri-terminal switch 53 is delayed by the time specified by the controlling circuit 56, whereby phase can be controlled. PA0 2) FIG. 2 shows another configurational example of a phase control circuit using another photocoupler and FIG. 3 shows voltage waveforms at several key points in the same circuit. In FIG. 2, like numerals are allotted to identical elements with those shown in FIG. 1, and repeated description is omitted. This circuit uses a photocoupler 62 having a CDS on a light-receiving side thereof which is varied in its internal resistance by light, and a capacitor 63 connected to the CDS. An output current from the light-receiving side of the photocoupler 62 charges the capacitor 63 whereby a charged voltage V.sub.C increases, causing a trigger signal to output for turning on a bidirectional tri-terminal switch 53. A diac etc., is used as an output device element (trigger element) 61 for outputting the trigger signal. As shown in FIG. 3, when a current corresponding to an input voltage V.sub.B is made to flow through the photocoupler 62, the charged voltage V.sub.C increases as shown in the figure. When this charged voltage V.sub.C exceeds a turn-on voltage V.sub.S for the trigger element 61, the trigger signal is outputted to activate the bidirectional tri-terminal switch 53, whereby a voltage V.sub.0 is applied across the load 52. In this circuit, the duration until the trigger element 61 is turned on or the time taken for the charged voltage V.sub.C to reach the turn-on voltage V.sub.S, varies depending on the magnitude of the current flowing through the CDS of the photocoupler 62, which in turn depends upon the input voltage V.sub.B. This means that, in this configuration, phase control can be effected by varying the input voltage V.sub.B.
One of the examples of the thus configurated phase control circuit is disclosed in Japanese Patent Application Laid-open Hei 5 No.54,977, and therefore publicly known.
The configurations 1) and 2) using a conventional photocoupler has respective drawbacks as follows: The configuration 1) needs three kinds of controlling circuitries 55, 56 and 57 to generate pulses for phase control. That is, as the pulse-generating timing must be set up by these circuitries, this complicates the circuit configuration and increases the number of parts.
The configuration 2) needs a number of parts such as a photocoupler, a trigger device, a capacitor, a bidirectional tri-terminal switch etc., increasing the number of parts, to thereby make the device bulky.